1. Field of the Invention
The present invention relates to the enhancement of viewing angle of liquid crystal displays, and in particular to a viewing angle enhancement film and a thin film transistor liquid crystal display (TFT-LCD) device incorporating the film.
2. The Related Arts
TFT-LCD device is a type of LCD device that employs TFT technology to achieve the presentation of images. Simply put, a TFT-LCD device involves a liquid crystal layer sandwiched between two glass substrates. A color filter film is configured on the upper glass substrate whereas TFTs are configured in the lower glass substrate. When electricity is conducted through the TFTs to produce electrical fields, the liquid crystal molecules are twisted by the electrical fields, thereby altering the polarization of light passing through. Additionally, a polarizer film can be configured in the TFT-LCD device so as to control the dark or bright states of pixels, and the emission of polarized light from the pixels, thereby achieving the desired presentation of images.
The problem of the existing technology is that, when back light passes through the polarizer film and TFTs, the light would become directional. In other words, most of the light emits perpendicularly from the screen. Therefore, when the LCD device is viewed from an angle, sometimes the presented image cannot be seen, and sometimes only purely white or purely black image can be seen.
FIG. 1 provides relationships between viewing angle and brightness, and between viewing angle and color coordinates, for a white image on an ordinary LCD device. From the leftmost diagram of FIG. 1, when the viewing angle is greater than 100 degree, the brightness would drop below ⅓ of the brightness along the direction normal to the screen (0 degree). To achieve a greater brightness, such as ½ of the brightness along the normal direction, the viewing angle has to be rather narrow. From the two diagrams in the middle and to the right of FIG. 1, one can see that color shift is more severe under a larger viewing angle.
On the other hand, consumers continuously demand even higher quality from LCD devices. And, as the dimension of LCD devices is getting larger, more people would be sharing a single LCD device. Therefore, the enhancement of viewing angle is of great concern to manufacturers.